1. Field of the Invention
The present invention relates to a system and method for setting up and calibrating an optical reader system.
2. Background Information
Optical readers are found in many types of systems, including scanners, copy machines, and document readers, such as, e.g., reader systems for processing markings in an image of a form, such as a lottery playslip. Lottery playslips include, e.g., a card, a ticket, or other printed media that indicates a player's lottery number selections. The playslips are used by a player to purchase a lottery ticket having player-indicated lottery number selections. The markings on lottery playslips are processed, e.g., to determine the numbers selected by a player for an upcoming lottery drawing.
Optical reader systems commonly include a motor that drives a document that is in contact with an illuminating bar positioned across the width of the document. As the document is driven past the illuminating bar, the bar scans the entire width and length of the document. Illumination is typically provided from light emitting diodes (LEDs) distributed along the length of the bar, but other illumination sources also may be used. Light or photo-sensitive receivers also are distributed along the length of the bar and are positioned to receive light that is reflected from the document as it passes the bar. In this environment, each photo-sensitive receiver represents a pixel and the intensity of the reflected light corresponds to the scene on the document; and, generally, more light is reflected from light areas and less from dark areas. Typically, the photo-sensitive receivers are photo-transistors, though other photo-sensitive devices may be used; and the output levels of the photo-transistors correspond to the intensity of the light that is received. The photo-sensitive transistors are electronically scanned across the width of the document. Herein, “scanned,” “read out”, “sampled”, and “clocked out” may be used interchangeably, and “light-sensitive” and “photo-sensitive” and combinations thereof are used interchangeably.
Calibrating an optical reader system for optimum operation is important for maintaining the integrity and the commercial competitiveness of any practical system. The photo-sensitive devices should allow for a wide linear gray scale dynamic range. That is, the device outputs an approximately linear signal that distinguishes dark levels from the lighter levels with many gray levels therebetween.
In a lottery environment, for example, an optical reader system is incorporated into an instant ticket lottery terminal and the reader's main function is to interpret the marks made by a player on a lottery playslip. An uncalibrated reader will produce a less uniform image of the playslip and, consequently, present a very good risk that a player's marks on the playslip may be missed or misinterpreted. By properly calibrating a reader, the playslip image is flattened and the marks on the slip are more clearly read and more accurately interpreted; thus, making the reader and lottery terminal more reliable.
Some calibration techniques currently know in the art include turning off the light source and shading the document so that the photo-sensitive devices receive no light. According to this technique, a “dark current” (which reflects leakage or droop that some photo-sensitive devices exhibit) is measured and a correction factor developed. In some respects, this correction is suspect in that optically scanning an item does not occur with no light.